Good article & good to get another perspective.
However, our experience when buying in the Bay Area, the banks were very diligent on checking the funds & supporting paperwork & also pulling credit.
I was last in the market 4 years ago. One loan agent did pre-approval just by the phone. She asked about our income, downpayment, etc. That was it. She just emailed her pre-approval letter. Obviously no diligence done.
However, it was competitive market (and still is). So we ended up getting pre-qualification letter from a bank. For that, it is like getting a loan, so had to prepare all docs: tax returns, income statement, bank statements, etc.
So our offers, we showed proof of downpayment (bank statement) to the seller. And the seller contacted the bank loan agent to confirm the pre-qualification letter. That is what it took when we had to go up against all-cash and 80% down.